1. Field of the Invention
The present invention relates to a photoelectric conversion device and its manufacturing method, in particular, to a photoelectric conversion device using a substrate on which photoreceptor pixels each having a photo diode and a thin-film transistor are arranged in array, and its manufacturing method.
2. Description of Related Art
Photo-sensors, which are photoelectric conversion devices, are flat panels equipped with a TFT array substrate on which photo diodes that convert visible rays into electricity and thin-film transistors (TFTs) are arranged. Such photo-sensors have been applied to and widely used in contact image sensors, radiographic display devices, and the likes. In particular, flat-panel radiographic display devices (herein after called “FPDs (Flat Panel Detectors)”), which are constructed by disposing a scintillator that converts X-rays into visible rays on an TFT array substrate, are considered to be promising devices that can be applied to the medical industry and the like.
In the field of X-ray diagnostic imaging, either or both of the precise images (still images) and the real-time image observation (moving images) have been used according to their purposes. For the shooting of still images, X-ray films are still predominantly used. Meanwhile, for the shooting of moving images, image-pickup tubes (image intensifier) in which a photomultiplier tube is combined with a CCD are used. Although X-ray films have a high spatial resolution, their sensitivity is low. Therefore, they can be used only for the shooting of still images. Further, the X-ray films have a drawback that they require a development process after the shooting, thus lacking in immediacy. Meanwhile, although image-pickup tubes have high sensitivity and thus be able to be used for the shooting of moving images, their spatial resolution is low. Further, since the image-pickup tubes are vacuum devices, they have a drawback that the upsizing of the devices is limited.
There are two modes of the FPDs, i.e., an indirect conversion mode in which X-rays are converted into light by a scintillator such as CsI and then the light is converted into an electrical charge by a photo diode, and a direct conversion mode in which X-rays are converted directly into an electrical charge by a X-ray sensing element typified by Se. The indirect conversion mode has higher quantum efficiency and a better signal/noise ratio (S/N ratio) in comparison to the direct conversion mode. Therefore, in the indirect conversion mode, fluoroscopy and/or image-taking can be performed with fewer radiation doses. Configurations and manufacturing methods of array substrates for indirect conversion mode FPDs have been disclosed in the past (for example, Japanese Unexamined Patent Application Publication No. 2000-101920).